*{
    margin: 0;
    padding: 0;
}
body{
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    background-color: #666;
}
.container{
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;  
    overflow: hidden;
    position: relative;
    width: 300px;
    height: 500px;
    background-color: darkgrey;
    border-radius: 20px;
    box-shadow: 15px 15px 10px rgba(33, 45, 58, 0.3);
}
.container form{
    display: flex;
    flex-direction: column;
    justify-content: space-around;
    align-items: center;
    margin-top: 20%;
    width: 100%;
    height: 200px;
    z-index: 1;
}
.container  h1{
    color: #000;
    z-index: 1;
}
.userBx{
    padding-left: 5px;
    width: 60%;
    height: 40px;
    outline: none;
    border: none;
    border-bottom: 1px solid #ffffff;
    background: none;
    color: #fff;
}
.userBx::placeholder{
    color: white;
}
.submit{
    width: 40%;
    height: 35px;
    outline: none;
    border: 1px solid #fff;
    border-radius: 10px;
    background: none;
}

/*鼠标进入和离开的样式*/
.container .in{
    position: absolute;
    top: 0;
    left: 0;
    display: block;
    width: 0;
    height: 0;
    border-radius: 50px;
    background-color: mediumpurple;
    transform: translate(-50%, -50%);
    animation: in 0.5s ease-out forwards;
}
.container .out{
    position: absolute;
    top: 0;
    left: 0;
    display: block;
    width: 200%;
    height: 200%;
    border-radius: 50px;
    background-color: mediumpurple;
    transform: translate(-50%, -50%);
    animation: out 0.5s ease-out forwards;
}
/*鼠标进入和离开的动画*/
@keyframes in{
    0%{
        width: 0;
        height: 0;
    }
    100%{
        width: 200%;
        height: 200%;
    }
}
@keyframes out{
    0%{
        width: 200%;
        height: 200%;
    }
    100%{
        width: 0;
        height: 0;
    }
}